1. Field of the Invention
The present invention relates to a power output apparatus having an internal combustion engine and a motor generator that is mechanically connected with the internal combustion engine and applies a significant load onto the internal combustion engine.
2. Description of the Related Art
Hybrid power output apparatuses having an internal combustion engine and a motor generator have recently been proposed as the power output apparatus, in which the motor generator is mechanically linked with the internal combustion engine and applies a significant loading torque to the internal combustion engine. The hybrid power output apparatuses include series-type hybrid power output apparatuses and parallel-type hybrid power output apparatuses. In the series-type hybrid power output apparatus, the power of the internal combustion engine is not directly transmitted to the drive shaft, but is regenerated in the form of electric power by the motor generator that is mechanically linked with the internal combustion engine. In the parallel-type hybrid power output apparatus, on the other hand, both the power of the internal combustion engine and the power of the motor generator are transmitted to the drive shaft. In one example of the parallel-type hybrid power output apparatus, the power output from the internal combustion engine is divided into the power portion transmitted to the drive shaft and the power portion transmitted to the motor generator. A second motor connected with the drive shaft is driven with the electric power generated by the motor generator, so that a required power is output to the drive shaft.
In the hybrid power output apparatus, the driving condition of the internal combustion engine is controlled by the parameters characteristic of the internal combustion engine, such as the quantity of fuel supply, as well as the loading torque and the revolving speed of the motor generator that is connected with the internal combustion engine. The power of the motor generator is output to the drive shaft. While there is a requirement for outputting the torque to the drive shaft, the internal combustion engine may be at a stop, at an idle, or in a motoring state to be forcibly rotated by the motor generator.
In the hybrid power output apparatus, however, a shock or an impulsive vibration for a relatively short time period may occur in the transient period when the driving condition of the internal combustion engine is shifted from the loaded driving state, in which a load is applied to the internal combustion engine by the motor generator, to the non-loaded driving state, in which no load is applied to the internal combustion engine. The driver and the passenger feel the shock when the hybrid power output apparatus is mounted on the vehicle. This damages the good ride of the hybrid vehicle.
In the parallel-type hybrid power output apparatus that uses gears for the power distribution mechanism, rattling noise of the gears may occur in the transient period. Since the hybrid power output apparatuses have been proposed just recently, such problems have not yet been even pointed out.